The present invention relates to graft, graft-block, block-graft, and star-shaped copolymers and continuous methods of making graft, graft-block, block-graft, and star-shaped copolymers.
In recent years, great attention has been paid to graft copolymers, because of their unique molecular architecture, particular morphology, and increased number of applications (Rempp et al., J. Anionic Polymerization, McGrath, Ed., ACS Symposium Series 166, American Chemical Society, Washington, D.C. (1981); Sawamoto, Int. J. Polym. Mater. 15:197 et seq. (1991); Lubnin et al., J. Macromol. Sci, Pure Appl. Chem. A31:1943 et seq. (1994); Hashimoto et al., Polym. J. 22:312 et seq. (1990); Geetha et al., Macromolecules 26:4083 et seq. (1993)). They have been widely used for the preparation of compatibilizers for polymer blends (Oshea et al., Polymer 35:4190 et seq. (1994); Hagazy et al., J. Polym. Sci., Polym. Chem. 31:527 et seq. (1993); Osman et al., Polym. Int. 36:47 et seq. (1996); Yang et al., J. Biomed. Mater. Res. 31:281 et seq. (1996); Grutke et al., Macromol. Chem. Phys. 195:2875 et seq. (1994); Eisenbach et al., Macromolecules 28:2133 et seq. (1995)), membranes for separation of gases or liquids (Yamashita et al., J. Appl. Polym. Sci. 40:1445 et seq. (1990); Ruckenstein et al., Macromolecules 30:6852 et seq. (1997); Se et al., Makromol. Chem., Macromol. Symp. 25:249 et seq. (1989)), hydrogels (Se et al., Macromolecules 30:1570 et seq. (1997)), drug deliverers (Zhang et al., Macromolecules 31:746-752 (1998)), and thermoplastic elastomers (Aoshima et al., Macromolecules 22:1009 et seq. (1989)). A number of methods have been employed for their synthesis, such as the macromonomer method (Se et al., Macromolecules 30:1570 et seq. (1997); Zhang et al., Macromolecules 31:746-752 (1998); (Aoshima et al., Macromolecules 22:1009 et seq. (1989); Kishimoto et al., Macromolecules 22:3877 et seq. (1989); Kamigaito et al., Macromolecules 24:3988 et seq. (1991); Zhang et al., J. Polym. Sci., Polym. Chem. 35:2901 et seq. (1997)), radiation-induced polymerization (Varshney et al., Macromolecules 23:2618 et seq. (1990); Aoshima et al., Polym. Bull. 13:229 et seq. (1985); Norhay et al., Block Copolymers Academic, New York (1977)), ring-opening olefin metathesis polymerization (Fayt et al., Macromolecules 20:1442 et seq. (1987)), polycondensation reaction (Varshney et al., Macromolecules 25:4457 et seq. (1992)), and iniferter-induced polymerization (Kunkel et al., Makromol. Chem., Macromol. Symp. 60:315 et seq. (1992)). However, the living polymerization technique is undoubtedly most suitable for the preparation of well-defined graft copolymers, in which both the backbone and the side chains possess designed molecular weights and narrow molecular weight distributions and the position, the number of side chains, and the composition of the graft copolymer can be controlled.
The advances in living polymerization have made the design and preparation of multiple-composition copolymers, such as block and graft copolymers, possible (Rempp et al., J. Anionic Polymerization, McGrath, Ed., ACS Symposium Series 166, American Chemical Society, Washington, D.C. (1981); Sawamoto, Int. J. Polym. Mater. 15:197 et seq. (1991); Lubnin et al., J. Macromol. Sci, Pure Appl. Chem., A91:1943 et seq. (1994)). Numerous block copolymers can be prepared by the sequential monomer addition technique. However, it is more difficult to prepare graft copolymers than block copolymers. Although a number of graft copolymers have been obtained (Hashimoto et al., Polym. J. 22:312 et seq. (1990); Geetha et al., Macromolecules 26:4083 et seq. (1993); Oshea et al., Polymer 35:4190 et seq. (1994); Hagazy et al., J. Polym. Sci., Polym. Chem. 31:527 et seq. (1993); Osman et al., Polym. Int. 36:47 et seq. (1996); Yang et al., J. Biomed. Mater. Res. 31:281 et seq. (1996); Grutke et al., Macromol. Chem. Phys. 195:2875 et seq. (1994); Eisenbach et al., Macromolecules 28:2133 et seq. (1995); Yamashita et al., J. Appl. Polym. Sci. 40:1445 et seq. (1990)), it was difficult to control the molecular weights of the backbone and side chains, the positions of the side chains, and their number. Even using a living polymerization technique, the graft copolymer was generally synthesized by a discontinuous route (Ruckenstein et al., Macromolecules 30:6852 et seq. (1997); Se et al., Makromol. Chem., Macromol. Symp. 25:249 et seq. (1989); Se et al., Macromolecules 30:1570 et seq. (1997)), in which the precursor polymer had to be separated from the polymerization solution and purified carefully. For example, Se and co-workers (Se et al., Macromolecules 30:1570 et seq. (1997)) prepared a well-defined block-graft copolymer using the living anionic polymerization method. A block copolymer consisting of polystyrene and poly-((4-vinylphenyl)dimethylvinylsilane) and living polyisoprene were first prepared separately, and their coupling reaction generated a graft copolymer. In this method, the unreacted polyisoprene had to be removed by repeated dissolution and precipitation. Besides the tedious and difficult process, the unavoidable introduction of impurities did not allow one to obtain a pure and well-defined graft copolymer. Recently, a graft copolymer was prepared consisting of a polymethacrylate backbone and poly(alkyl vinyl ether) side chains (Ruckenstein et al., Macromolecules 30:6852 et seq. (1997)), by using the anionic polymerization of 1-(isobutoxy)ethyl methacrylate followed by the cationic polymerization of alkyl vinyl ether. However, in that method, the poly(1-(isobutoxy)ethyl methacrylate) had to be isolated from its tetrahydrofuran (THF) solution and purified carefully before it was used as macroinitiator for the cationic polymerization of alkyl vinyl ether.
The incorporation of functional groups into the surface of polymer materials or into polymeric chains can greatly improve their properties. For instance, the direct introduction of new functionalities onto a polymer surface or the surface modification by grafting can change the surface hydrophilicity, hydrophobicity, biocompatibility, and adhesion (Galina, Adv. Polym. Sci., 137:1 et seq. (1998)). The direct synthesis of well-defined graft copolymers with functional groups can control not only the properties of the surface, but also the molecular parameters, architecture, and composition of the polymer. However, well-defined graft copolymers containing functional side chains have seldom been prepared because of the difficulty in preparing living polymers with polar substituents.
The present invention is directed to overcoming the above-noted deficiencies in the prior art.
The present invention relates to a continuous method of preparing a block-graft or star-shaped copolymer. This method involves providing a living polymer, mixing the living polymer with a first monomer under conditions effective to produce a block copolymer, wherein the first monomer comprises a living polymerization site and a living polymerization initiation site, and mixing the block copolymer with a second monomer under conditions effective to produce a block-graft or star-shaped copolymer.
The present invention also relates to a block-graft or star-shaped copolymer having the formula: 
where n is an integer, m is an integer, r is an integer, and n, m, and r are a predetermined polymerization degree, R an alkyl, R1 is selected from the group consisting of an alkyl, 2-chloroethyl, 2-acetoxyethyl, and 2-methacryloyloxyethyl, and M1 is selected from the group consisting of styrene, xcex1-methyl styrene, butadiene, isoprene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and tert-butyl methacrylate.
Another aspect of the present invention is a continuous method of preparing a graft copolymer. This method involves mixing a first monomer and a second monomer under conditions effective to produce a copolymer of the first and second monomers, wherein the first monomer comprises a polymerization site and a polymerization initiation site, and mixing the copolymer with a third monomer under conditions effective to produce a graft copolymer.
Yet another aspect of the present invention is a graft copolymer having the formula: 
where m is an integer, n is an integer xe2x89xa70, R is the same or different and is selected from the group consisting of an alkyl, acetoxyethyl, chloroethyl, and methacryloyloxyethyl, and M1 is selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, and tert-butyl methacrylate.
The present invention further relates to a continuous method of preparing a graft-block copolymer. This method involves mixing a first monomer and a second monomer under conditions effective to produce a copolymer of the first and second monomers, wherein the first monomer comprises a living polymerization site and a living polymerization initiation site, mixing the copolymer with a third monomer under conditions effective to produce a graft copolymer, and mixing the graft copolymer with a fourth monomer under conditions effective to produce a graft-block copolymer.
Another aspect of the present invention is a graft-block copolymer having the formula: 
where m is an integer, n is an integer, R is the same or different and is selected from the group consisting of an alkyl, acetoxyethyl, chloroethyl, and methacryloyloxyethyl, R1 is he same or different and is selected from the group consisting of an alkyl, acetoxyethyl, chloroethyl, and methacryloyloxyethyl, and M1 is selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, and tert-butyl methacrylate.
The present invention discloses improved continuous methods for the synthesis of copolymers with controlled molecular weight and narrow molecular weight distribution, in which lengthy polymer separation and purification is no longer needed. In addition, the methods of the present invention allow the preparation of more complex molecular architectures, such as block-graft copolymers where: (1) the molecular weights of the backbone and side chains, hence the total molecular weight of the copolymer, can be controlled; (2) the side chains of the block-graft copolymer are located only in one part of the backbone, and their number can be selected; and (3) both the backbone and the side chains possess narrow molecular weight distributions.